Abstract: Several preparation methods were used to synthenize fluorinated polyimide with bigger molecular weight so that a better preparation was found after the structure of the fluorinated polyimide was tested by IR absorbing spectrum.Based on thermogravimetric analysis and differential scanning calorimetry,it was proved that the material might decompose at 530℃ with high thermal stability and have wave-guide thermal character.Finally the linearity relations of refractive index and temperature or refractive index and content of fluorin were proved through measurement of the material.